The cellular industry is experiencing an unprecedented demand for mobile data. This is expected to continue to increase in the coming years. One option to meet this growing demand is to dedicate more of the radio frequency spectrum to mobile data communication. However, much of the useful spectrum is below 6 GHz due to propagation characteristics, and this portion of the spectrum is already jointly consumed by commercial communication systems and RADAR.
Regulatory bodies in several countries including the United States are considering the sharing of under-utilized spectrum as a viable solution to the spectrum scarcity problem. In the United States, the Federal Communications Commission (FCC) is expected to propose a rule that allows the sharing of 150 MHz of spectrum in the 3.5 GHz S-band between commercial communications systems with low-powered small cells and RADAR. For successful sharing of the spectrum, techniques to mitigate harmful interference to both of these systems are needed.
A straightforward way of achieving sharing of the spectrum is by spatial separation of communications systems and RADAR installations. The National Telecommunications and Information Administration (NTIA) has proposed exclusion zones between RADAR and communications systems that would protect the RADAR incumbents from any harmful interference from the secondary users. A second approach for spectrum sharing that uses Dynamic Spectrum Access (DSA) includes communications devices sensing the presence of incumbent RADAR in a given frequency channel and vacating the channel.